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<title>Testing DBI backends</title>

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<h1 class="title toc-ignore">Testing DBI backends</h1>
<h4 class="author">Kirill Müller</h4>



<p>This document shows how to use the DBItest package when implementing
a new DBI backend or when applying it to an existing backend. The
DBItest package provides a large collection of automated tests.</p>
<div id="testing-a-new-backend" class="section level2">
<h2>Testing a new backend</h2>
<p>The test cases in the DBItest package are structured very similarly
to the sections in the “backend” vignette:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" tabindex="-1"></a><span class="fu">vignette</span>(<span class="st">&quot;backend&quot;</span>, <span class="at">package =</span> <span class="st">&quot;DBI&quot;</span>)</span></code></pre></div>
<p>Like the “backend” vignette, this vignette assumes that you are
implementing the <code>RKazam</code> package that has a
<code>Kazam()</code> function that creates a new <code>DBIDriver</code>
instance for connecting to a “Kazam” database.</p>
<p>You can add the tests in the DBItest package incrementally, as you
proceed with implementing the various parts of the DBI. The DBItest
package builds upon the testthat package. To enable it, run the
following in your package directory (after installing or updating
<code>devtools</code>):</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb2-1"><a href="#cb2-1" tabindex="-1"></a>devtools<span class="sc">::</span><span class="fu">use_testthat</span>()</span>
<span id="cb2-2"><a href="#cb2-2" tabindex="-1"></a>devtools<span class="sc">::</span><span class="fu">use_test</span>(<span class="st">&quot;DBItest&quot;</span>)</span></code></pre></div>
<p>This creates, among others, a file <code>test-DBItest.R</code> in the
<code>tests/testthat</code> directory. Replace its entire contents by
the following:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb3-1"><a href="#cb3-1" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">make_context</span>(<span class="fu">Kazam</span>(), <span class="cn">NULL</span>)</span>
<span id="cb3-2"><a href="#cb3-2" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">test_getting_started</span>()</span></code></pre></div>
<p>Now test your package with <code>devtools::test()</code>. If you
followed at least the “Getting started” section of the DBI “backend”
vignette, all tests should succeed.</p>
<p>By adding the corresponding test function to your
<code>tests/test-DBItest.R</code> file <em>before</em> implementing a
section, you get immediate feedback which functionality of this section
still needs to be implemented by running <code>devtools::test()</code>
again. Therefore, proceed by appending the following to
<code>tests/test-DBItest.R</code>, to include a test case for the
forthcoming section:</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb4-1"><a href="#cb4-1" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">test_driver</span>()</span></code></pre></div>
<p>Again, all tests should succeed when you are done with the “Driver”
section. Add the call to the next tester function, implement the
following section until all tests succeed, and so forth.</p>
<p>In this scenario, you are usually interested only in the first error
the test suite finds. The <code>StopReporter</code> of
<code>testthat</code> is most helpful here, activate it by passing
<code>reporter = &quot;stop&quot;</code> to <code>devtools::test()</code>.
Alternatively, call the relevant <code>DBItest::test_()</code> function
directly.</p>
<p>The tests are documented with the corresponding functions: For
instance, <code>?test_driver</code> shows a coarse description of all
tests for the “Driver” test case. Test failures will include the name of
the test that is failing; in this case, investigating the documentation
or the source code of the DBItest package will usually lead to the cause
of the error.</p>
<p>Not all tests can be satisfied: For example, there is one test that
tests that <code>logical</code> variables survive a write-read roundtrip
to the database, whereas another test tests that <code>logical</code>
variables are converted to <code>integer</code> in such a case. Tests
can be skipped by adding regular expressions for the tests to skip as
character vector to the call, as in the following<a href="#fn1" class="footnote-ref" id="fnref1"><sup>1</sup></a>:</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb5-1"><a href="#cb5-1" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">test_driver</span>(<span class="at">skip =</span> <span class="fu">c</span>(</span>
<span id="cb5-2"><a href="#cb5-2" tabindex="-1"></a>  <span class="st">&quot;data_type&quot;</span>           <span class="co"># Reason 1...</span></span>
<span id="cb5-3"><a href="#cb5-3" tabindex="-1"></a>  <span class="st">&quot;constructor.*&quot;</span>,      <span class="co"># Reason 2...</span></span>
<span id="cb5-4"><a href="#cb5-4" tabindex="-1"></a>  <span class="cn">NULL</span></span>
<span id="cb5-5"><a href="#cb5-5" tabindex="-1"></a>))</span></code></pre></div>
<p>Some other reasons to skip tests are: - your database does not
support a feature - you want to postpone or avoid the implementation of
a feature - the test takes too long to run.</p>
</div>
<div id="testing-an-existing-backend" class="section level2">
<h2>Testing an existing backend</h2>
<p>For an existing backends, simply enabling all tests may be the
quickest way to get started. Run the following in your package directory
(after installing or updating <code>devtools</code>):</p>
<div class="sourceCode" id="cb6"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb6-1"><a href="#cb6-1" tabindex="-1"></a>devtools<span class="sc">::</span><span class="fu">use_testthat</span>()</span>
<span id="cb6-2"><a href="#cb6-2" tabindex="-1"></a>devtools<span class="sc">::</span><span class="fu">use_test</span>(<span class="st">&quot;DBItest&quot;</span>)</span></code></pre></div>
<p>This creates, among others, a file <code>test-DBItest.R</code> in the
<code>tests/testthat</code> directory. Replace its entire contents by
the following:</p>
<div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">make_context</span>(<span class="fu">Kazam</span>(), <span class="cn">NULL</span>)</span>
<span id="cb7-2"><a href="#cb7-2" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">test_all</span>()</span></code></pre></div>
<p>The notes about “Kazam” and skipping tests from the previous section
apply here as well. The <code>test_all()</code> function simply calls
all test cases.</p>
</div>
<div id="external-testing" class="section level2">
<h2>External testing</h2>
<p>DBItest is currently geared towards usage as part of a package’s test
suite. With some effort it is possible to test a database backend
against a custom database. This can help verify that your database
installation gives expected results when accessed with DBI with specific
connection arguments.</p>
<p>The example below shows how to run tests with the RSQLite
backend.</p>
<div id="preparation" class="section level3">
<h3>Preparation</h3>
<p>First, we need to define a test context. It contains:</p>
<ul>
<li>a connector that describes how to establish the database connection,
see <code>?DBI::`DBIConnector-class`</code> for details,</li>
<li>tweaks, see <code>?tweaks</code>,</li>
<li>tests skipped by default, as a character vector.</li>
</ul>
<p>Database backends that use DBItest for testing usually have a file
<code>test/testthat/helper-DBItest.R</code> or
<code>test/testthat/test-DBItest.R</code> where a call to
<code>make_context()</code> can be found. The help for
<code>make_context()</code> already contains an example that works for
RSQLite. Adapt it to your needs.</p>
<p>The <code>make_context()</code> function must be called before any
tests can run.</p>
<div class="sourceCode" id="cb8"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb8-1"><a href="#cb8-1" tabindex="-1"></a><span class="fu">library</span>(DBItest)</span>
<span id="cb8-2"><a href="#cb8-2" tabindex="-1"></a></span>
<span id="cb8-3"><a href="#cb8-3" tabindex="-1"></a>tweaks <span class="ot">&lt;-</span> <span class="fu">tweaks</span>(</span>
<span id="cb8-4"><a href="#cb8-4" tabindex="-1"></a>  <span class="at">constructor_relax_args =</span> <span class="cn">TRUE</span>,</span>
<span id="cb8-5"><a href="#cb8-5" tabindex="-1"></a>  <span class="at">placeholder_pattern =</span> <span class="fu">c</span>(<span class="st">&quot;?&quot;</span>, <span class="st">&quot;$1&quot;</span>, <span class="st">&quot;$name&quot;</span>, <span class="st">&quot;:name&quot;</span>),</span>
<span id="cb8-6"><a href="#cb8-6" tabindex="-1"></a>  <span class="at">date_cast =</span> <span class="cf">function</span>(x) <span class="fu">paste0</span>(<span class="st">&quot;&#39;&quot;</span>, x, <span class="st">&quot;&#39;&quot;</span>),</span>
<span id="cb8-7"><a href="#cb8-7" tabindex="-1"></a>  <span class="at">time_cast =</span> <span class="cf">function</span>(x) <span class="fu">paste0</span>(<span class="st">&quot;&#39;&quot;</span>, x, <span class="st">&quot;&#39;&quot;</span>),</span>
<span id="cb8-8"><a href="#cb8-8" tabindex="-1"></a>  <span class="at">timestamp_cast =</span> <span class="cf">function</span>(x) <span class="fu">paste0</span>(<span class="st">&quot;&#39;&quot;</span>, x, <span class="st">&quot;&#39;&quot;</span>),</span>
<span id="cb8-9"><a href="#cb8-9" tabindex="-1"></a>  <span class="at">logical_return =</span> <span class="cf">function</span>(x) <span class="fu">as.integer</span>(x),</span>
<span id="cb8-10"><a href="#cb8-10" tabindex="-1"></a>  <span class="at">date_typed =</span> <span class="cn">FALSE</span>,</span>
<span id="cb8-11"><a href="#cb8-11" tabindex="-1"></a>  <span class="at">time_typed =</span> <span class="cn">FALSE</span>,</span>
<span id="cb8-12"><a href="#cb8-12" tabindex="-1"></a>  <span class="at">timestamp_typed =</span> <span class="cn">FALSE</span></span>
<span id="cb8-13"><a href="#cb8-13" tabindex="-1"></a>)</span>
<span id="cb8-14"><a href="#cb8-14" tabindex="-1"></a></span>
<span id="cb8-15"><a href="#cb8-15" tabindex="-1"></a>default_skip <span class="ot">&lt;-</span> <span class="fu">c</span>(<span class="st">&quot;roundtrip_date&quot;</span>, <span class="st">&quot;roundtrip_timestamp&quot;</span>)</span>
<span id="cb8-16"><a href="#cb8-16" tabindex="-1"></a></span>
<span id="cb8-17"><a href="#cb8-17" tabindex="-1"></a><span class="fu">invisible</span>(<span class="fu">make_context</span>(</span>
<span id="cb8-18"><a href="#cb8-18" tabindex="-1"></a>  <span class="fu">new</span>(</span>
<span id="cb8-19"><a href="#cb8-19" tabindex="-1"></a>    <span class="st">&quot;DBIConnector&quot;</span>,</span>
<span id="cb8-20"><a href="#cb8-20" tabindex="-1"></a>    <span class="at">.drv =</span> RSQLite<span class="sc">::</span><span class="fu">SQLite</span>(),</span>
<span id="cb8-21"><a href="#cb8-21" tabindex="-1"></a>    <span class="at">.conn_args =</span> <span class="fu">list</span>(<span class="at">dbname =</span> <span class="fu">tempfile</span>(<span class="st">&quot;DBItest&quot;</span>, <span class="at">fileext =</span> <span class="st">&quot;.sqlite&quot;</span>))</span>
<span id="cb8-22"><a href="#cb8-22" tabindex="-1"></a>  ),</span>
<span id="cb8-23"><a href="#cb8-23" tabindex="-1"></a>  <span class="at">tweaks =</span> tweaks,</span>
<span id="cb8-24"><a href="#cb8-24" tabindex="-1"></a>  <span class="at">default_skip =</span> default_skip</span>
<span id="cb8-25"><a href="#cb8-25" tabindex="-1"></a>))</span></code></pre></div>
</div>
<div id="testing" class="section level3">
<h3>Testing</h3>
<p>Use <code>test_all()</code> to run all tests, and
<code>test_some()</code> to run a specific test that failed previously.
The <code>test_*</code> functions need to be run with a testthat
reporter to avoid stopping at the first error or warning. For
interactive use, the “progress” reporter gives good results. In the
example below, the “location” and “stop” reporters are combined. Review
<code>?testthat::Reporter</code> for a list of reporters.</p>
<div class="sourceCode" id="cb9"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb9-1"><a href="#cb9-1" tabindex="-1"></a>DBItest<span class="sc">::</span><span class="fu">test_some</span>(<span class="st">&quot;get_query_atomic&quot;</span>)</span></code></pre></div>
<pre><code>## Test passed</code></pre>
<p>DBItest relies heavily on metaprogramming. Unfortunately, this means
that a failing test may give no indication of the reason for the
failure. The <code>test_some()</code> function now by default integrates
the new experimental <a href="https://github.com/r-dbi/dblog">dblog
package</a> package. It prints the DBI code that is executed as the
tests are run, as seen above.</p>
<p>Another way to scout for the reason of the problem is to review the
sources of DBItest and relate the test name (that is printed with each
failure) with the human-readable specification embedded with the test
code.</p>
<div class="sourceCode" id="cb11"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb11-1"><a href="#cb11-1" tabindex="-1"></a>testthat<span class="sc">::</span><span class="fu">with_reporter</span>(</span>
<span id="cb11-2"><a href="#cb11-2" tabindex="-1"></a>  <span class="fu">c</span>(<span class="st">&quot;location&quot;</span>, <span class="st">&quot;fail&quot;</span>),</span>
<span id="cb11-3"><a href="#cb11-3" tabindex="-1"></a>  DBItest<span class="sc">::</span><span class="fu">test_some</span>(<span class="st">&quot;get_query_atomic&quot;</span>)</span>
<span id="cb11-4"><a href="#cb11-4" tabindex="-1"></a>)</span></code></pre></div>
<pre><code>## Start test: DBItest: Result: get_query_atomic
##    [success]
##    [success]
##    [success]
##    [success]
##    [success]
##    [success]
##    [success]
## End test: DBItest: Result: get_query_atomic</code></pre>
</div>
</div>
<div class="footnotes footnotes-end-of-document">
<hr />
<ol>
<li id="fn1"><p>The terminating <code>NULL</code> allows appending new
lines to the end by copy-pasting an existing line, without having to
take care of the terminating comma.<a href="#fnref1" class="footnote-back">↩︎</a></p></li>
</ol>
</div>



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